Network Planning Strategy for Evolving Network Architectures

Transcription

1 INTERNATIONAL TELECOMMUNICATION UNION Telecommunications Development Bureau (BDT) Network Planning Strategy for Evolving Network Architectures 10 October 2003 Riccardo Passerini, ITU-BDT Signalling Network Computer Aided Planning and Dimensioning COMPUTER AIDED PLANNING AND DIMENSIONING OF THE SIGNALLING NETWORK Main tasks of Signalling Network Planning: Determination/optimization of the Signalling Network Structure Determination of an optimised design of the routing data of each signalling point (Routing of Signalling Traffic) Dimensioning of the signalling link Set under consideration of network failures (failed route sets and Signalling points) Determination of Signalling Network Performance 2 1

2 COMPUTER AIDED PLANNING AND DIMENSIONING OF THE SIGNALLING NETWORK For Signalling Networks with more than 10 SP s/stp s the planning and dimensioning tasks can only be reasonably achieved by using computer aided planning and dimensioning Therefore a tool is required by means of which an optimized Signalling Network Planning can be realized by iterative steps Major Benefits - Stability and efficiency of signalling networks - Respect to routing and dimensioning - Solving the problematic of complexity of the CCSS7 routing tables. 3 COMPUTER AIDED PLANNING AND DIMENSIONING OF THE SIGNALLING NETWORKS Example of Planning Tool may fulfill the following requirements: - Hardware: Powerful PC or Work Station Color screen Key board and mouse input Simple printer and graphic printer or plotter 4 2

3 COMPUTER AIDED PLANNING AND DIMENSIONING OF THE SIGNALLING NETWORK -Software: SW-platform independent on operating system object-oriented programming for reuse of codes, simple extensions, easy generation of program variants, easy to maintain, enhanced SW reliability Desktop similar to standard (e.g. XWINDOWS) Handling language English 5 Signalling and Trunk Networks Packet-switched queuing system Alternate route for CCSS7 link failure (changeover/changeback) Transient and partial Signalling Link occupation only during the signalling events (e.g. Call Setup, Release) Different routing in signalling and trunk network Circuit-switched loss system Alternate routes for trunk group blocking (overflow) Permanent circuit occupation during the call holding time Signalling Network Trunk Network 6 3

4 Concepts and Advantages of CCSS7 Signalling channel and the associated signalling equipment is time-shared between many speech channels more efficient signalling Datagram mode of operation (like packet-switching) and layered design of CCSS7 protocol faster, more reliable and more flexible for new applications (e.g. IN services) Logical and possibly physical separation between signalling and trunk network more flexible since signalling network independent from existing trunk network hierarchy 7 Benefits of CCSS7 Signalling Big variety of messages High flexibility referring to new services (ISDN, IN, Mobile GSM) Secured transmission of signalling messages One CCSS7 channel replaces about 80 CAS* channels Economical savings referring to channel costs (1/30 = 3%, 16th channel in PCM30) CCSS7 - a cost-effective, adequate signalling method for modern and future digital networks * CAS = Channel Associated Signalling 8 4

5 Signalling Operating Modes Associated mode A B equal utilization of network higher reliability smaller end-to-end delay Signalling relation e.g. for speech channels Signalling link Quasi-associated mode C A STP B SP more economical for low loaded links simpler administration simpler for planning As a consequence there may be given a load-threshold for the decision on the signalling mode for an individual link set which leads to: Associated mode A Mixed mode C B Quasi-associated 9 Routing in Signalling and Trunk Network Signalling Network C C A A D B CCSS7 Operating Mode: Associated for A B Quasi-associated for C D Trunk Network B D The path used by the Signalling Messages may be different from the path in the trunk network, because signalling and trunk network are logically independent! 10 5

6 Planning tasks Definition of user requirements Signalling services (application parts) to be provided by the Signalling Network Signalling load defined by traffic model and volume per signalling service Possible network topology Reliability and delay requirements ISUP INAP MAP Signalling network planning issues Topology & Structure (e.g. no. & location of STPs) Signalling Routing Tables Dimensioning of Signalling Link Sets Calculation of load (link & node) Reliability & End to End Signalling delay 11 CCSS7 Planning Issues Determination of target network structure: number and location of STP Comparison of several alternative solutions Iterative optimisation of the final configuration acc. to criteria referring to security, technical constraints, costs etc. Definition of intermediate extension stages and transition strategy Generation of routing tables (free from circular routing) Definition of appropriate planning parameters, e.g. operating mode threshold, planned load per link, per node etc Investigation of failure scenarios (sensitivity analysis) Generation of planning results (routing tables, link set diagram) 12 6

7 Signalling Network Planning and Optimization Process (Overview) Input of the network Creation of the routing plan Check-up of the routing plan All destinations accessible? No circular routing? Addition of routes to ensure accessibility, deletion of routes to avoid circular routing Dimensioning Calculation of number of link sets Calculation of SP-, STP-load Creation of routing plan optimum by introduction of quasi-associated signalling referring to max. STP-load Check-up of performance requirements Reliability? End-to-end delay? Introduction of additional routes to fulfil requirements Output per SP/STP Routing table Link set diagram Performance values (load, no. of hops) 13 PLANNING PROCESS OF SIGNALLING NETWORKS INPUT: Numbering plan, data structure of host Network, traffic data, reliability performances, etc.. Automatic generation of routing tables Optimization of routing tables: addition, change, deletion of routes Optimization of network structure: addition, change, deletion of SPs/STPs and/or link sets Check of accessibility of all SPs/STPs + Routes OR Check for circular routes Distribution of signalling load - Routes + Routes Dimensioning of link sets Calculation and check of SP/STP-load Check of reliability of signalling relations Check of end-to -end -delay + Routes +/- Routes + Routes +/- Routes Output: node and link set parameters link set diagrams routing tables SP/STP- and linkset-load performance values 14 7

8 Computer Aided Signalling Network Planning Advantages Software takes over time consuming work (calculations etc.) Fast and easy comparison of scenarios Cost-effective design possibilities Targets of Computer Aided CCSS7 Quick set up of new planning projects (network structure) changes and extensions, especially if network size > 10 nodes Support for route set creation process (circular routing) Use in network management centers Purchase to network operators 15 Characteristics of Signalling Planning tools Sophisticated algorithms for defining precise amounts of equipment (TS) providing assistance in planning of CCSS7 networks by means of Consideration of common characteristics of CCSS7 systems Representation of one MTP network with nodes able to serve as SP or integrated SP/STP or exclusive STP Allowance for several users (services, e.g. ISUP, IN) with individually related demand and traffic model Graphical user interface for network representation Intuitive, menu-driven handling Iterative activation of functions possible 16 8

9 Input Data of Planning Tool-CCSS7 Global network parameters (e.g. several numbering structures) Modelling of Network elements Signalling points (SP) with/without integrated transfer functionality (SP/STP) and stand-alone (STP) Service matrices with corresponding individual traffic model to define the traffic demand (superposition of several services possible): Call - matrix (Call/s) BHCA - matrix (busy hour call attempts) MSU - matrix (MSU/s) Trunk group matrix (Number of trunks) Traffic value matrix (Erl carried) Routing table of the signalling points (optional, manual) Trunk groups as actual or potential link sets Topology (nodes, link sets) create, select, move, delete, etc. 17 Signalling Traffic Sources and Modelling Signalling of telephony network (ISUP) given as trunk matrix with traffic values trunk matrix with number of trunks (average utilisation) Signalling of other services (e.g. IN) given as call matrix BHCA matrix MSU matrix Traffic model in each case making allowance for: MSU length percentage of effective (answered) calls (ASR) * mean holding time * MSU per effective/ineffective call in forward/backward direction * * where applicable 18 9

10 Routing Functions Automatic creation of route sets (standard and alternate routes) Options:generation for all or only for marked route sets load sharing between routes of equal (hop) length Algorithm: search for shortest path routes Route search restrictions: consideration of homing definitions (in quasi-associated operating mode) Import of already existing/implemented routing data Check of circular routing Check of full accessibility of nodes Allowance for maximum number of hops per relation Visualisation of route sets (different colours for normal and alternate routes) 19 Circular Routing: - Loops of Signalling messages CCSS7-protocol does not provide any information about code and number of transit-nodes (STPs) which have been already passed. CCSS7-routing tables are independent of the origin of a signalling relation. >> Risk of circular routing! << The generation of appropriate routing tables without signallingmessage cycling is one of the main tasks of a Signalling Planning Tool A 1 2 D 1 C 2 TFP TFP D or all links connected to D fail: 2 1 B Cycle A->C->B->A In spite of TFP message SP/STP 1 standard route 2 alternate route 20 10

11 Automatic Creation of Routing Tables Possible Methods "non-hierarchical" (shortest path routing) "hierarchical" (hierarchical multi-plane-routing "enhanced hierarchical" (shell-routing) 21 Load Distribution and Dimensioning of Link Sets Load distribution due to entries in the route sets (standard routes) and to signalling traffic (service matrices) Calculation of total relative load of each node (SP- and STP-function processing performance) Dimensioning of link sets with allowance for planned load per link, e.g. 0.2 Erl minimum and maximum no. of links per link set given (fixed) or existing (already installed) number of links threshold for switchover associated/quasi-associated operating mode 22 11

12 Performance Criteria: Reliability and Delay Reliability Calculation of the reliability of each signalling relation with the planning tool via the reliability values of nodes (SP/STP) and links the current routing plan Delay A precise calculation per signalling relation requires the calculation of delay of signalling links (see ITU-T Q.706) knowledge of processing times in SP/STP (perhaps of different providers) ITU-T recommendation E.721 only contains target values of maximum number of passed network elements (nodes, links) 23 Presentation of Results On the screen Coloured presentation of load situation Precise load values per» SP/STP (MSU/s, Byte/s sent and received) Link Set (MSU/s, Byte/s forward and backward direction) Statistical overview of mean, minimum and maximum values On the paper or in a file Protocol of input data Link set diagrams Graphical plot of network Statistical data 24 12